Hypotonically induced calcium release from intracellular calcium stores

Area of Science:

• Cell Biology
• Physiology
• Biochemistry

Background:

• Osmotic cell swelling is linked to increased intracellular calcium (Ca2+).
• This Ca2+ rise is partly attributed to release from internal cellular stores.
• The precise mechanism of Ca2+ release during hypotonic stress was unclear.

Purpose of the Study:

• To investigate the response of non-mitochondrial Ca2+ stores to reduced cytoplasmic tonicity.
• To determine if hypotonic stress directly induces Ca2+ release from intracellular stores.
• To identify the pathway and regulatory factors involved in hypotonically induced Ca2+ release.

Main Methods:

• Experiments were conducted using permeabilized A7r5 cells.
• The study measured Ca2+ release from intracellular stores under hypotonic conditions.
• The involvement of specific receptors (inositol trisphosphate, ryanodine) and passive leak pathways was assessed.
• The effect of various divalent cations on Ca2+ release was evaluated.

Main Results:

• Direct Ca2+ release from intracellular stores was observed upon exposure to a hypotonic medium.
• This Ca2+ release was graded and did not involve inositol trisphosphate or ryanodine receptors.
• Ca2+ release occurred via a passive leak pathway.
• The release was inhibited by divalent cations, with Ni2+ and Co2+ being most potent.
• The phenomenon was also observed in intact A7r5 cells.

Conclusions:

• Intracellular Ca2+ stores can directly release Ca2+ in response to hypotonic stress.
• This novel mechanism operates independently of second messengers, suggesting stores act as osmosensors.
• The passive leak pathway is implicated in hypotonically induced Ca2+ release.
• This finding provides new insights into cellular volume regulation and calcium signaling.